As supporters of the Senate’s comprehensive immigration reform bill continue to mourn its collapse this week, key Republican backers must also brace for potentially stinging political repercussions from their party’s base.

Here’s a look at the fallout for congressional Republicans (not named McCain) most adversely impacted by the defeat of one of the Bush administration’s key domestic priorities:

South Carolina Sen. Lindsey Graham Like Sen. John McCain (R-Ariz.), Graham has styled himself as a maverick during his first term in the Senate. He helped draft the compromise immigration legislation and was one of its most outspoken backers.

And like McCain, his approval ratings have dipped since he took up immigration reform as a key issue. In a poll conducted in June, Graham scored just a 31 percent approval rating among South Carolina voters. More Republicans (45 percent) than Democrats (32 percent) disapproved of his performance.

The poll was conducted by InsiderAdvantage/Majority Opinion and surveyed 790 South Carolina voters on June 18 and 19.

Graham’s campaign questions the poll’s methodology but admits that the immigration bill has been unpopular throughout the state, particularly among Republicans.

Graham has drawn sharp criticism from conservative talk show hosts and the Republican faithful. Conservative talk show host Rush Limbaugh has referred to Graham as “Lindsey Grahamnesty,” while several South Carolina Republicans created the website DumpLindsey.org, designed to recruit potential challengers.

Graham, however, may not face the serious opposition that some critics once envisioned. State Sen. Greg Ryberg and state Senate Majority Whip Jim Ritchie are considered the most likely candidates to seriously challenge Graham from the right, but neither has publicly suggested he will run.

Suspended state Treasurer Thomas Ravenel, once considered a possible Graham GOP opponent, was recently indicted on cocaine distribution charges. None of the other leading Republicans statewide have suggested they would run against Graham. And the one announced challenger, businessman John Cina, has no political experience or name recognition in the state.

Meanwhile, Graham has $3.6 million in his Senate campaign account — a powerful financial disincentive for prospective opponents.

“If anyone takes Graham’s political experience and acumen for granted, they’re making a huge mistake. He’s incredible on the stump. He’s savvy,” said Luke Byars, state director for South Carolina Republican Sen. Jim DeMint. “He’s going to be a very tough person to campaign against if you take on that challenge.”

Florida Sen. Mel Martinez After being named chairman of the Republican National Committee — giving him a powerful bully pulpit for the party — Martinez wasn’t able to muster much political muscle in support of immigration reform.

And his backing of the bill has cost him politically back home, according to a just-released InsiderAdvantage poll. According to the poll, Martinez’s approval rating in Florida is now at 23 percent, while 47 percent disapprove of his performance. Thirty-one percent said they had no opinion.

The poll was conducted June 26 and 27 and interviewed 885 registered voters in Florida. It has a margin of error of plus or minus 3 percentage points.

“It really is as bad as it seems,” said InsiderAdvantage CEO Matt Towery. “This may be his nadir, his absolutely low point. Immigration is on the minds of the public [in Florida], and it didn’t have support in the state.”

Even Hispanic voters disapproved of the performance of Martinez, a Cuban-American, by a 2-1 ratio. Towery speculated that the Hispanic population in Florida, mainly comprising Puerto Rican and Cuban immigrants, “are thoroughly indigenous American demographic groups” and were “as threatened” by illegal immigration as the overall population.

Martinez doesn’t face reelection until 2010, when the heat over immigration may have subsided.

Rep. Tom Feeney (R-Fla.), a vigorous opponent of the immigration legislation, defended Martinez and doubted that his support would cost him — at least not in Florida.

“I think most people understand Mel has a unique background here,” said Feeney. “On this issue, he’s speaking from the heart.”

Arizona Sen. Jon Kyl Kyl was ranked as the most conservative senator by National Journal in 2006, so when he became one of the key supporters of the immigration legislation, he raised a few eyebrows among party activists.

According to state party spokesman Brett Mecum, over 95 percent of calls coming into the state party were against the legislation.

“It’s damaged him, but I don’t think it’s going to be anything permanent, especially given his conservative credentials,” Mecum said. “Ninety-nine percent of the time we agree with Senator Kyl — this was just one of those issues that the base of the party had a very large difference of opinion.”

Kyl, who isn’t up for reelection until 2012, may not have suffered much lasting political damage. But he may have lost his stature as a stalwart conservative, as he was upstaged by Sens. DeMint, John Cornyn (R-Texas) and David Vitter (R-La.), all of whom were prominent opponents of the legislation.

Utah Rep. Chris Cannon Cannon has faced fierce challenges from the right over the issue of immigration in the last two elections, and was hoping a compromise bill would defuse the issue and stave off challengers in his Provo-based district.

But with passion on the issue still running high, Cannon will again likely face a serious primary challenge. One high-profile primary challenger, Jason Chaffetz, former chief of staff to Gov. Jon Huntsman, has already entered the race.

“Immigration is one of those issues that is going to stick with a candidate for a long period of time," Towery said. "It replaced abortion, which was the litmus test to see if you were a real Republican. Now it seems the immigration bill is the new litmus test.”